SRC-3/PELP1 complexes drive stem-like phenotypes in luminal breast cancer

摘要 在结节阳性的患者中，乳腺癌复发仍然是一个重要的风险。乳腺癌的茎或茎- 类细胞(本文中的BCSCs)传播和逃避一线治疗，并在 患有晚期内分泌抵抗疾病的患者。本提案的目标是定义信令 驱动内分泌耐药的BCSCs出现和扩张的途径，目的是阻断 表观遗传学事件，以此为目标的肿瘤细胞群体。填补这一知识空白将为 用于阻断BCSCs并确保长期无病生存的干预措施。我们确认了染色质- 相关的类固醇受体(SR)转录辅助调节因子PELP1，作为BCSC扩张的中介。利用 经质谱鉴定，类固醇受体辅活化子-3，SRC-3(也称为AIB1)是一种新的 与核PELP1相比，与胞质的选择性相互作用。值得注意的是，PELP1增加了对 SRC-3在BC细胞中的表达，而SRC-3基因敲除则阻断了PELP1诱导的BCSC的扩张，这表明 活性PELP1/SRC3复合体在BCSC生长中的作用在后续研究中，我们发现细胞质 PELP1促进Thr24和Ser857上SRC-3的磷酸化。其他人的工作已经牵连到SRC-3 PSer857在乳腺癌转移中作为双功能激酶/磷酸酶关键底物的作用 PFKFB4.在相关工作中，我们证明了PELP1与两种雌激素都形成了结构性转录复合体 (ER)和孕激素(PR)受体在乳腺癌模型和患者肿瘤中的作用；PR- ER/PR/PELP1的ER磷酸化和基因调控需要B，而不是黄体酮 复合体，包括对他莫昔芬耐药重要的基因集。在这里，我们假设 ER/PR/PELP1/SRC-3复合体招募和放大关键的细胞质信号通路 类固醇受体(SR)调节的染色质重塑和重编程所需的表观遗传学事件 扩大耐药BCSC群体所需的转录本。我们将在以下方面测试这一假设 乳腺癌模型，并在以下具体目标： ·确定PELP1/SRC-3激活的信号通路对BCSC的扩增和治疗耐药至关重要。 ·确定PELP1/SRC-3复合体如何对SR转录本重新编程。 ·确定PELP1/SRC-3/SR协同作用是否促进体内肿瘤形成。 目前的治疗方法主要是抑制BC的增殖，但不能充分靶向BCSCs。了解 PELP1/SRC-3/SR信号转导机制和BCSCs可逆表遗传调控将揭示新的机制 针对该复合体(即，内质网以外)或下游信号转导所需组件的治疗 分子，阻止或逆转这一过程，从而显著影响患者的寿命 转移性乳腺癌。

Abstract Breast cancer recurrence remains a significant risk among node-positive patients. Breast cancer stem or stem- like cells (BCSCs herein) disseminate and evade first-line therapies, and account for high mortality among patients with advanced endocrine-resistant disease. The objective of this proposal is to define the signaling pathways that drive the emergence and expansion of endocrine-resistant BCSCs, with the goal of blocking epigenetic events to specifically target this population of tumor cells. Filling this knowledge gap will pave the way for intervention that blocks BCSCs and ensures long-term disease-free survival. We identified the chromatin- associated, steroid receptor (SR) transcriptional coregulator, PELP1, as a mediator of BCSC expansion. Utilizing mass spectrometry, we identified the steroid receptor coactivator-3, SRC-3 (also known as AIB1), as a novel and preferential interactor with cytoplasmic relative to nuclear PELP1. Notably, PELP1 increased activation of SRC-3 in BC cells, while SRC-3 knockdown blocked PELP1-induced BCSC expansion, suggesting an essential role for active PELP1/SRC3 complexes in BCSC outgrowth. In follow-up studies, we found that cytoplasmic PELP1 promotes the phosphorylation of SRC-3 on Thr24 and Ser857. Work of others has implicated SRC-3 pSer857 in breast cancer metastasis as a key substrate of the bifunctional kinase/phosphatase known as PFKFB4. In related work, we showed that PELP1 forms constitutive transcriptional complexes with both estrogen (ER) and progesterone (PR) receptors in breast cancer models and patient tumors; a scaffolding action of PR- B, but not progesterone, was required for ER phosphorylation and regulation of genes by ER/PR/PELP1 complexes, including gene sets important for tamoxifen resistance. Herein, we hypothesize that ER/PR/PELP1/SRC-3 complexes recruit and amplify key cytoplasmic signaling pathways that mediate epigenetic events required for chromatin remodeling and reprogramming of steroid receptor (SR)-regulated transcriptomes required for expansion of therapy resistant BCSC populations. We will test this hypothesis in breast cancer models and in the following Specific Aims: • Identify PELP1/SRC-3-activated signaling pathways essential for BCSC expansion and therapy resistance. • Determine how PELP1/SRC-3 complexes reprogram SR transcriptomes. • Determine if PELP1/SRC-3/SR cooperation promotes tumorigenesis in vivo. Current therapies primarily inhibit BC proliferation, but fail to adequately target BCSCs. Understanding the mechanisms of PELP1/SRC-3/SR signaling and reversible epigenetic regulation of BCSCs will reveal novel therapies that target the required components of this complex (i.e. other than ER) or downstream signaling molecules and prevent or reverse this process, thus significantly impacting on the longevity of patients with metastatic breast cancer.